The present invention relates to high speed lithographic printing techniques and more particularly to direct-to-press imaging systems for use in forming printing images directly on a printing cylinder used in printing operations.
In accordance with conventional lithographic printing practices for printing continuous webs of paper, ink in desired image patterns is conveyed from inked printing plates that are attached to plate cylinders and thence by means of a blanket cylinder having a more or less compressible surface onto the paper. The printing plate carries a differentiated image on a dimensionally stable substrate such as an aluminum sheet. The imaged aluminum plate is secured to the plate cylinder by a mechanical lock-up mechanism which defines positional register between the plate and the surface of the cylinder. When new images are to be printed, the mechanical lock-up system is released so that the printing plate carrying the old image can be removed and discarded and a newly imaged printing plate can be positioned and locked into place for the next print run.
In the past, press-ready lithographic printing plates have been prepared off-press by forming the required ink receptive image areas and water receptive non-image areas on suitable printing plate surfaces in a manner similar to photographic development. Preparation can be by means of hand operation or by means of readily available automatic developing and processing machines. Once having been imaged, printing plates generally are hand carried to the vicinity of the printing press and fixedly attached to the printing cylinder by press operators using the lock-up mechanism built into the cylinder itself. Although the attachment of the printing plates to the printing cylinder is generally a manual operation, robotic means can be used for positioning and securing printing plates.
Operations involving off-press imaging and manual mounting of printing plates are relatively slow and cumbersome. On the other hand, high speed information processing technologies are in place today in the form of pre-press composition systems which can electronically handle all the data required for directly generating the images to be printed. Almost all large scale printing operations currently utilize electronic pre-press composition systems that provide the capability for direct digital proofing using video displays and visible hard copies produced from digital text and digital color separation signals stored in computer memory and which can also be used to express page-composed images to be printed in terms of rasterised digitized signals. Consequently, conventional imaging systems whereby the printing images are generated off-press by means of paste-up, mechanical layout, photographic film-making, or plate exposure and development operations which create a physical printing plate that must be mounted on a printing cylinder constitute or induce inefficient and expensive bottle-necks in printing operations.
It is therefore an object of the present invention to provide a system whereby digitized graphic information typical of electronic pre-press composition systems can be bridged directly to conventional high speed, high volume printing presses without the necessity for handling any form of hard copy, film material or printing plate.
It is another object of the present invention to provide a system for applying digitally formed master images directly onto master-image cylinders and for automatically erasing such images from such cylinders so that new images can be applied thereto.
It is a further object of the present invention to minimize the dependence upon operator skill and the susceptibility to human error in the conveyance of image information from electronic prepress composition systems to the actual printing presses.
It is yet another object of the present invention to eliminate or reduce the need for intermediate image processing materials and equipment such as photographic film, metallic or other printing plates, chemical process systems associated with film or plate making and the like.
It is a yet further object of the present invention to eliminate the need for mechanical lock-up and pin register systems and the like used in mounting printing plates onto printing cylinders.